Place oven rack in middle position. Heat to 350°F. Lightly coat a 9-in. tart pan with removable bottom with nonstick spray. Have a baking sheet ready (to get filled pan in and out of oven more easily).

Crust: Process cookies in food processor until reduced to fine crumbs. Add coconut, orange peel and egg white; process until crumbs are moistened. Press over bottom and up sides of prepared pan. Bake 15 minutes or until lightly browned. Cool on a wire rack.

Filling: Using a whisk, stir 3⁄4 cup sugar and the cornstarch in a large bowl until combined. Stir in eggs, butter, 3⁄4 cup sour cream, grated peels and juices until blended (mixture may look curdled). Place pan with baked crust on baking sheet; slowly pour in filling.

Bake 35 minutes or until filling sets. While tart bakes, stir the 1 tsp sugar into sour cream remaining in tub. Scrape into a small ziptop plastic bag.